The long term objectives of the research are to understand the behavior and role of calcium metabolism in mammalian neurones, including the mutual interaction of transmembrane calcium fluxes and intracellular enzyme systems. The proposed research will use the calcium indicator dye arsenazo III to measure directly voltage dependent changes of intracellular calcium concentration in a mammalian neurone, the NIE-115 mouse neuroblastoma clone. The proposed experiment is to inject the calcium indicator dye arsenazo III into single voltage clamped NIE-115 mouse neuroblastoma cells. The optical transmittance of the cell will be monitored during depolarization. A rapid space scanning microphotometer will be used to map the distribution of calcium channels over the surface of single NIE-115 cells. Calcium that enters neurones through voltage dependent channels acts as a second messenger, controlling and modulating a wide range of cellular processes including synaptic transmission. The antiepileptic and antiarrhythmic drug phenytoin may exert its effects by blocking voltage dependent calcium channels. The actions of phenytoin on epileptic focal neurones are closely matched by its effect on NIE-115 cells, therefore the NIE-115 cell serves as a useful model of epileptic focal neurones.